The Food-Crushing Reflex and Its Inhibition

Round 1

Reviewer 1 Report

Thank you for the opportunity to review this interesting paper.

My overall impression is that this will be a useful and stimulating contribution to the literature on vertebrate feeding neuromechanics, pending some impoirtant improvements.

First, the English is pretty good, but in a few places it needs some work. For example, in the Abstract the term “feed” should probably be “feedback” or “feed forward” depending on the context. Line 60: disclude is not a word. Line 67: “a unilaterally located”. Line 72-3 should read “A part … is conveyed”. Line 197: should be “study demonstrating” or “study to demonstrate”.Fenotype should be phenotype.  I suggest that the author has someone read through it to fine tune the English.

Second, as noted below, muscle spindles were certainly NOT present in early vertebrate jaw muscles and probably did not evolve until the origin of tetrapods. The author needs to acknowledge this and modify their hypothesis to posit some other kind of intramuscular receptor. One line 239 they write about “Piezo1 or Piezo2 type of calcium channel units” as a possible substitute. This idea may be worth developing, but we will need to see more details. Reference 26 and 27 are not appropriate for that task. Similarly, we know virtually nothing about sensory feedback from the oral cavities of fish. They must have it because many of them engage in significant intra-oral food processing, but we know nothing about it. This should be acknowledged as well.

Third, I think the review of the differential wiring and functioning of reflexes subserving anterior and posterior biting in humans is useful and interesting. But extending this anterior-vs-posterior dichotomy to early gnathostomes is too much of a stretch (no pun intended) and isn’t necessary. I think its plausible that there were feedback mechanisms in early vertebrate jaws, modulating muscle activity to ensure efficient biting without too much tooth breakage, but this see-saw model is unlikely to be correct. The muscle attachment reconstruction in Figure 1 (middle skull) is almost certainly incorrect; this animal could not have opened its mouth. I think the biomechanics in Figure 4 are not correct. Yes, the lines of action of different parts of temporalis intersect the toothrow in different places, meaning that their force vectors have different actions on the jaw joint depending on bite point, but all parts of temporalis will stretch if there is any actual distraction of the joint. If there is evidence that I am wrong about that, I am happy to be corrected.

Line by line comments:

Line 46: I presume that this sentence refers to humans, but maybe they mean all mammals. This should be specified. I do not think that this reflects the consensus: the cortex is certainly involved in monitoring and contributing to control of jaw and tongue movements, but the idea that masticatory movements are “caused” by corticobulbar fibers is not correct as written (do fibers cause things?), and rats can chew without cortical contributions, and they can modulate the force generated in anticipation of test strip hardness (See Hidaka et al, 1997).

Line 114: Figure 114: It is not clear to me how different parts of a pennate muscle can differentially elevate different parts of the jaw. If an adducting muscle attaches to the jaw it will generate an elevating torque on the entire jaw. In addition, the reconstructed jaw muscles in the middle figure (attaching near the tip of the jaw) would prevent the jaw from opening at all. If someone has suggested they attach there, please give the reference.

Line 148: The author writes as if this information is known about early vertebrates, but it is not. They cite Surayanarayna et al.’s paper, but that says nothing about early vertebrate feeding, and it focuses on the lamprey, which is agnathous and is probably highly derived relative to early jawless vertebrates. This all should at least be acknowledged.

Line 219: I am not clear as to why we are reading about development of the teeth. I understand that the author wants to posit different functional units for anterior and posterior dentition, but why is development relevant for that?

Line 239: the most problematic aspect of this paper is the assertion that early vertebrates had muscle spindle sin their jaw muscles, something for which there is no evidence. Many people have looked and, with one dubious exception, no-one has found muscle spindles in fish muscles. The exception is one report of one spindle in one salmon from Japan. This has never been replicated. The assumption that spindles were present in early vertebrate jaw muscles is unsubstantiated. Reference 26 does not help because it is about myelin, not about spindles. Reference 27 is about monkeys.

Line 318, Figure 4: I think the biomechanics here are flawed. Yes, different parts of temporalis have different lines of action relative to the bite point, but if the condyle of the jaw rotates downwards during posterior biting (i.e., puts the joint in tension), then surely ALL the parts of the temporalis will be stretched. This critique also applies to Figure 1.

First, the English is pretty good, but in a few places it needs some work. For example, in the Abstract the term “feed” should probably be “feedback” or “feed forward” depending on the context. Line 60: disclude is not a word. Line 67: “a unilaterally located”. Line 72-3 should read “A part … is conveyed”. Line 197: should be “study demonstrating” or “study to demonstrate”.Fenotype should be phenotype.  I suggest that the author has someone read through it to fine tune the English.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

hello

is this paper a review or a hypothesis? its lacking a good structure for a review - if hypothesis it should be written in this matter

if its a hypothesis where is the H0???

introduction is very poorly written and not structurised

introduction shoul focud on anatomy of muscles, TMJ, and chewing mechanism and not about a nuts-cake

what does an act of god impact on chewing or cusp fracture? it sounds more like a  philosophical paper, rather then hypothesis.......

at the end of paragraph the aim of the paper is not highlighted fully, and unclear for a basic reader

if its a review, in what style its written? what kind of papers had been searched world-wide, how and which were inclued and what excluded from the study? and why?

are presented figures, drawn by author or are they copied from someplace?

the conclusion section is too long - it should 5-7 brief points for a basic reader

the rest of the sentences please move before the conclusion

citation list needs to be re-arranged and written according to the mdpi rules

its interesting, but written in a very chaotic form, which a basic reader will not understand a simple thing

please consider a major revision, and more clear presentation of the review and its form

thank you

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

The article "The Food-Crushing Reflex and its Inhibition" has been written in an accessible manner, although the terminology used is quite advanced. It introduces the reader to the subject matter related to the stomatognathic system and the innate reflexes controlled by our nervous system. The article fills a gap in our knowledge about the processes associated with chewing and the evolution of these reflexes. While we already know a lot, further research is necessary to understand this complex process fully. Nevertheless, the article is inspiring and certainly encourages further exploration of this fascinating field of science.

Author Response

Please, see the attachment

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Thank you for the opportunity to review this paper again. Some of my most important criticisms were not addressed. I personally think the paper presents a theory that is unlikely to be correct.

1.     As with the previous version, there are still many typos and awkwardly phrased English. I suggested an English speaker read the paper and help with the corrections. This has not been done, It still should be. Here I give corrections for some where meaning is unclear, but otherwise leave this up to the author and the editor to resolve.

Line 9: change “multiplicate” to “multiply”; line 14, change “jaw” to “jaws”

Line 26, change “to” to “in”

Line 298: what is “emryonally” supposed to be?

Line 322: change “exemplaries” to “examplars”, change “was” to “were”

2.     I have some suggested changes to text to clarify meaning.

Line 27, instead of “jaw movements” do you mean “bite force”?

Line 28, change “overrun” to “override”? I actually do not think these reflexes override the muscle activity patterns; rather, they work with them.

Line 84: change “unless” to “were it not”

Line 162: change “subjected” to “transmitted”

Line 340: what is meant by “overlapping to the opposite hemisphere”? Brainstems are not usually described as having hemispheres. (see line 345 as well).

Lines 429-430: should “whereabout” read “location”?

Line 463: I to not think kinematics is the right term. If the theory is about bite force, the word should probably be “kinetic”

3.     Figure 1 is still anatomically incorrect. Yes, we do not know exactly where the muscles attached, but we can be very confident that they didn’t attach anterior to the food item in the middle figure. The authors ignored my previous comments. The figure should be altered to resemble the vector presentation in Figure 4.

4.     Again, there is no reason to believe that extant fishes have muscle spindles in their jaw muscles, the Maeda paper notwithstanding. Others have looked and not found them.

definitely needs some clarity here and there

Author Response

Response to reviewer comments

I am grateful for the expert reviewer comments. The reviewing process is a platform for dialogue and I clearly understand that in the earlier versions of this manuscript I have not made my point clear enough. Re-reading my text again I admit the specific flaws of my text as indicated with the specific line numberings by the reviewer. Thank you for your advice, these mistakes are now corrected, as suggested by the reviewer. The previous revisions of the text, that I made in the end of June appear red. The September revisions are marked green.

“Bite force” is definitively better expression than “jaw movements”. I am thankful for the comments. For a non-native English speaker, to understand semantic distinction between “overrun” and “override” is hard (I still don’t really understand the difference). Definitively I agree, in the context of my message “transmitted” sounds more authentic than “subjected”. The same I now find true is about the semantics between the “unless” and “were it not”.

I was not aware of that “hemisphere” should not be used in the context of midbrain structures, but I certainly will keep that in mind in the future. The “whereabouts” sounds beautiful to me but now I understand it is not appropriate for scientific text. Also, I acknowledge the comment on the distinction between “kinetics” and “kinematics” with gratitude.   

The most important comment was, however, that the figure and legends did not succeed in bringing out the essence of my hypothesis. As a result, I have redrawn the “Dunkleosteus cracking a trilobite”, Figure 1.  I now clearly understand that the instantaneous transcendences of the classes 1,2, and 3 lever systems of mastication should have been more thoroughly elaborated for the reader. Instead of asking the reader to peek out for Figure 4 (of which the earlier wordings of its legend, I humbly admit, was quite incomprehensible), I have added the Figure 2 two depict the counter-directional jolts of jaw muscles undergoing food crushing. Another hypothetical principle presented in Figure 2, the need for neural control of differentially oriented jaw muscles, should be in agreement with the established findings concerning the activity of lateral pterygoid muscle motor units in horizontal jaw movements. I think the concept of “heterogenous activation of differentially oriented motor units of jaw muscles according to functional needs” was first presented by Uchida et al (ref 19 of the present version of manuscript). Greg Murray has further elucidated this concept in his review article on the functions of the lateral pterygoid muscle (Australian Dental Journal, 2004, 49: 1-8).

I agree with the reviewers statement about the apparent absence of spindles of teleost jaw muscles. Yes, originally, I was elated finding Maeda’s article. It seemed to fit in so nicely. Yet, what do we know about distant body parts communicating with muscle activity command centres in the spine, brain stem and cortex? It is true, my hypothesis is essentially dependent of some sort of a muscle stretch-receptor. Perhaps, some brave visionary investigator of the future might be encouraged to endeavour this matter.

I admit the quality of my English language is far from perfect and needs some clarity here and there, and in the words between. I would like to add a special acknowledgment to my friend Pertti Väisänen for his patience to undergo full three hours of telephone conversation checking my revised text, line by line, discussing the dots and commas, and the “ofs” and “fors”.

Yours sincerely,

The Author 

Reviewer 2 Report

thank you for the comments 

Author Response

Response to reviewer comments

I am grateful for the expert reviewer comments. The reviewing process is a platform for dialogue and I clearly understand that in the earlier versions of this manuscript I have not made my point clear enough. Re-reading my text again I admit the specific flaws of my text as indicated with the specific line numberings by the reviewer. Thank you for your advice, these mistakes are now corrected, as suggested by the reviewer. The previous revisions of the text, that I made in the end of June appear red. The September revisions are marked green.

“Bite force” is definitively better expression than “jaw movements”. I am thankful for the comments. For a non-native English speaker, to understand semantic distinction between “overrun” and “override” is hard (I still don’t really understand the difference). Definitively I agree, in the context of my message “transmitted” sounds more authentic than “subjected”. The same I now find true is about the semantics between the “unless” and “were it not”.

I was not aware of that “hemisphere” should not be used in the context of midbrain structures, but I certainly will keep that in mind in the future. The “whereabouts” sounds beautiful to me but now I understand it is not appropriate for scientific text. Also, I acknowledge the comment on the distinction between “kinetics” and “kinematics” with gratitude.   

The most important comment was, however, that the figure and legends did not succeed in bringing out the essence of my hypothesis. As a result, I have redrawn the “Dunkleosteus cracking a trilobite”, Figure 1.  I now clearly understand that the instantaneous transcendences of the classes 1,2, and 3 lever systems of mastication should have been more thoroughly elaborated for the reader. Instead of asking the reader to peek out for Figure 4 (of which the earlier wordings of its legend, I humbly admit, was quite incomprehensible), I have added the Figure 2 two depict the counter-directional jolts of jaw muscles undergoing food crushing. Another hypothetical principle presented in Figure 2, the need for neural control of differentially oriented jaw muscles, should be in agreement with the established findings concerning the activity of lateral pterygoid muscle motor units in horizontal jaw movements. I think the concept of “heterogenous activation of differentially oriented motor units of jaw muscles according to functional needs” was first presented by Uchida et al (ref 19 of the present version of manuscript). Greg Murray has further elucidated this concept in his review article on the functions of the lateral pterygoid muscle (Australian Dental Journal, 2004, 49: 1-8).

I agree with the reviewers statement about the apparent absence of spindles of teleost jaw muscles. Yes, originally, I was elated finding Maeda’s article. It seemed to fit in so nicely. Yet, what do we know about distant body parts communicating with muscle activity command centres in the spine, brain stem and cortex? It is true, my hypothesis is essentially dependent of some sort of a muscle stretch-receptor. Perhaps, some brave visionary investigator of the future might be encouraged to endeavour this matter.

I admit the quality of my English language is far from perfect and needs some clarity here and there, and in the words between. I would like to add a special acknowledgment to my friend Pertti Väisänen for his patience to undergo full three hours of telephone conversation checking my revised text, line by line, discussing the dots and commas, and the “ofs” and “fors”.

Yours sincerely,

The Author 

Round 3

Reviewer 2 Report

thank you for all the corrections

now its better